Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 240810

National Weather Service Jackson KY
410 AM EDT Wed May 24 2017

.SHORT TERM...(Today through Thursday)
Issued at 410 AM EDT WED MAY 24 2017

Surface analysis shows an area of surface low pressure continues
to deepen across Middle TN this morning. This as an upper level
wave in the lower MS Valley based on WV SAT rides NE providing
plenty of forcing for ascent across the TN and OH Valley. This
will also drive the aforementioned surface low pressure NNE
likely just NW of the CWA. This will probably drive a more
occluded front across the region and lead to a solid chance of
showers and thunderstorms from late morning into this afternoon.
The low track certainly has our attention, as it would favor
backed winds near the surface. The real issue at hand will be the
large scale forcing could inhibit building any instability this
afternoon with more debris clouds streaming into the region.
However, despite the caveat if we do see clearing and subsequently
more instability organized convection would be likely given ample
shear, with effective values running in the 30 to 40-knot range.
Also the low level backing mentioned above would combine with low
LCLs and effective SRH approaching 200 m^2/s^2 leading to a
isolated tornado risk. However, the main risks with any stronger
storms that could get going would be damaging winds and large
hail given the potential for rotating updrafts. The CAMs remain
complicated and solutions continue to differ probably owing to the
large scale ascent. The HRRR TLE does offer a shot of seeing
severe hail, but the CIPS are lack luster when it comes to climo
for this setup. Also given the deep moisture also can not rule
out the potential for isolated instances of flash flooding.

This upper level closed low will continue to wrap up today and
deepen across the Ohio Valley. The low pressure will track north
and this will lead to a lull in the precipitation this evening.
Did not go no POPs tonight but would not be surprised if that is
the case. However, this system will become vertically stacked
across the Ohio Valley. This will send an area of PVA and low
level convergence SE toward the region by dawn Thursday. An area
of showers will accompany this area of lift and ride across the
region on Thursday. Then surface pressure and height rises are
left in the wake.

Temperatures today will be dependent on clearing, but lower 70s
will probably be the story. Did hedge below the blended guidance
Thursday given the lowering 850mb temps and cloud cover.

.LONG TERM...(Thursday night through Tuesday)
Issued at 410 AM EDT WED MAY 24 2017

Wrap-around moisture on the backside of a departing upper low and
surface low across the Ohio Valley will continue the threat for rain
showers through Thursday evening, before a brief stint of ridging
and subsidence filters into eastern Kentucky for the end of the
week. This will bring some patchy fog to the valleys of eastern
Kentucky, moreso in the Bluegrass and Lake Cumberland regions,
Friday morning as clearing occurs earlier in the night. A
ridge/valley temperature split should be in store as well as a dry
Friday takes shape with seasonable temperatures in the mid-upper 70s.

This reprieve from the wet weather will be short-lived as backing
flow aloft takes shape downstream of an upper low rotating into
Manitoba, along with attendant troughiness extending through the
Great Plains into the Desert Southwest. A surface low pressure
system will ride up the Ohio Valley as eastern Kentucky sits in the
warm sector, bringing renewed chances of showers and thunderstorms
through Memorial Day weekend. Numerous shortwave perturbations look
to be entrenched in the prevailing southwest flow regime, leading to
mid level cooling and large scale forcing for ascent. Eastward
movement of this system into the Great Lakes late this weekend will
bring a cold front through the Ohio Valley and toward eastern
Kentucky later Sunday into Sunday night. While storms on Saturday
should exhibit more of a discrete nature, increasing larger scale
forcing later Sunday will likely lead to a linear storm mode.
Therefore, the more widespread threat of any severe weather, most
notably a damaging wind threat, would come later Sunday with this
latter development. Still some details to be ironed out regarding
southern extent of the greater upper level forcing along with the
exact degree of destabilization that will materialize.

Dry and somewhat cooler conditions should ensue for Memorial Day,
prior to another round of showers and thunderstorms arriving Tuesday
as another upper low swings into the upper Midwest and western Great
Lakes on the heels of the weekend system. A subsequent cold frontal
passage will further lower temperatures through the 70s as
subsidence builds in for midweek.


.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)

The period will be met with VFR to airfield mins in relative
subsidence between upper level waves. This will lead to varying
TAFs overnight for most of the sites and particularly sites that
have increased low level moisture form earlier convection. While
most of the shower activity has diminished this hour more activity
will develop under deepening surface low toward dawn and onward.
By this afternoon would suspect CIGs and VIS would lower again to
MVFR/IFR at times in heavier shower and thunderstorm activity.
Most areas will continue to see light winds, but perhaps some
isolated higher gusts are possible with any thunderstorms.




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